1. Field of the Invention
The present invention relates generally to apparatus and methods for introducing devices to target locations within body lumens and cavities. In particular, the present invention relates to introducing catheters and methods which are used to provide large-diameter access lumens to target locations disposed along or at the distal end of tortuous paths.
Introducer sheaths and catheters are commonly used to provide endoluminal and/or percutaneous access to remote target locations in a variety of medical procedures, including intravascular procedures, laparoscopic procedures, and other minimally invasive procedures. Of specific interest to the present invention, the endovascular placement of vascular grafts for the treatment of abdominal aortic aneurysms has been proposed, where the graft may be inserted into the aorta via an antegrade or retrograde arterial approach. Such endovascular graft placement will require the use of a relatively large graft placement catheter, typically having an outer diameter in the range from 4 mm to 10 mm. Such large placement catheters will require correspondingly large introducing catheters or sheaths, typically having an internal lumen diameter which is at least slightly larger than the outer diameter of the placement catheter. The placement and use of such large-diameter introducing catheters or sheaths will be problematic in several respects.
In particular, the antegrade path into the subclavian artery, through the aortic arch, and into the thoracic aorta is quite tortuous. While the path can be readily negotiated by conventional intravascular guide wires, such guide wires have very small diameters and are not sufficiently strong to permit introduction of a large diameter introducing sheaths thereover. To overcome this problem, it would be possible to employ an introducing sheath having an integral steering mechanism. Such sheaths could be introduced around even the very tight curves encountered in the transition from the subclavian artery to the aortic arch. The incorporation of a steering mechanism, however, necessarily reduces the lumen area of the sheath which is ultimately available for accommodating the graft-placement catheter.
Other problems which arise when introducing sheaths are used for aortic access include the design of the hemostasis valve. The hemostasis valve must be able to accommodate very small devices, such as guide wires, as well as the very large graft-placement catheter. The body of the sheath must have a very thin wall (to maximize available area in the access lumen), and a very smooth lumen to permit the passage of the graft-placement catheters without sticking or constriction of the catheter. Additionally, placement of vascular grafts through an introducing sheath located in the abdominal aorta is further made difficult by the relatively high blood flow rate through the aorta. Moreover, the ability to anchor the vascular graft within the aorta and/or adjoining iliac arteries can be problematic and require additional devices which are difficult to provide through the limited area of the access lumen.
For these reasons, it would be desirable to provide improved catheter introducing systems and methods, including catheter sheaths, sheath steering mechanisms, hemostasis valves, and the like, which overcome at least some of the deficiencies described above. The introducing sheaths should have a large lumen diameter, typically being at least 4 mm, to accommodate large diameter graft-placement catheters, should have good hoop strength to avoid kinking or collapse of the sheath when bent around tight curves, and should have good column and tensile strengths to avoid deformation when the graft-placement catheter is passed through the lumen. The sheath steering mechanisms should provide for a high degree of lateral deflection at the distal end of the sheath but should not take up lumen area which is necessary for subsequent passage of large diameter catheters. The hemostasis valves should be able to accommodate both small diameter devices, such as guide wires, and the large diameter catheters while still maintaining a tight seal around the catheter to prevent leakage.
2. Description of the Background Art
A steerable sleeve for use in combination with a flexible catheter is described in DE 39 20 707. U.S. Pat. No. 4,976,688 shows a steerable sheath structure. European Patent Application 488 322 shows a tubular device having a variable curvature controlled by differential pressure. Other catheter and device-steering mechanisms are described in U.S. Pat. Nos. 5,109,830; 5,098,412; 5,019,040; 4,983,165; 4,066,070; and 3,941,119.
A large-diameter introducer sheath having metal-ribbon reinforcement and a proximal hemostasis valve is described in U.S. Pat. No. 5,180,376. Devices covered by the '376 patent are sold by Arrow International, Inc., Reading, Pa. 19605, under the name super Arrow Flex.TM. percutaneous sheath introducer set with integral side port/hemostasis valve. Other reinforced tubular catheter designs are described in U.S. Pat. Nos. 5,279,596; 5,275,152; 5,226,899; 5,221,270; 5,221,255; 5,069,217; 4,985,022; and 4,411,655.
U.S. Pat. No. 5,207,656, discloses a hemostasis valve having a foam member for sealing against a catheter passed therethrough. The foam member has a lubricant absorbed in an open-cell foam structure. U.S. Pat. No. 4,475,548, discloses a foam sealing member for use in an endotracheal tube. European patent application 567,141 describes a trocar valve assembly which may include a flexibly resilient material for reception of an instrument passed through the valve. Other hemostasis and similar valve structures are described in U.S. Pat. Nos. 5,338,313; 5,300,034; 5,279,597; 5,242,425; 5,222,948; 5,215,537; 5,167,636; 5,127,626; 5,104,389; and 4,177,814.